When an operator requests a propulsion direction change (i.e., forward or backward propulsion) of a machine, the control system may initially control a drive train to retard motion in the current direction. The control system may initiate such drive train retarding by adjusting the transmission (e.g. downshifting) thereby using parasitic losses to slow the machine down. However, adjusting the transmission to initiate drive train retarding may increase the speed of the engine. If the operator has commanded a target engine speed close to the maximum desirable engine speed, the fueling system may struggle to respond quickly enough (i.e., reduce fueling rate) to prevent the engine from increasing above a maximum desirable engine speed when the drive train retarding is initiated.
One method that has been employed to prevent an operator input from causing the engine speed to exceed a desired limit is disclosed in U.S. Pat. No. 6,755,177 (the '177 patent) issued to Woolford et al. on Jun. 29, 2004. The system disclosed in the '177 patent includes a controller that continuously monitors the engine speed requested by the operator and compares the requested engine speed with a predetermined engine speed. If the requested engine speed is greater than the predetermined engine speed, the system operates in a speed limit mode. In the speed limit mode, the controller maintains the fueling rate to the engine at a level that prevents the actual engine speed from exceeding the predetermined engine speed.
Although the system disclosed in the '177 patent may prevent an operator request from causing the engine speed to exceed a threshold when the requested engine speed is above the threshold, the system's usefulness may be limited during propulsion direction changes. In particular, during propulsion direction changes, an engine speed can rapidly increase above an operator requested engine speed. If the operator requests an engine speed close enough to a threshold engine speed, the actual engine speed may exceed the threshold during the rapid increase associated with the propulsion direction change. Therefore, waiting until the operator requests an engine speed that exceeds the threshold before overriding the operator request may not prevent the operator request from causing the engine speed to exceed the threshold engine speed during propulsion direction changes.
The disclosed system is directed to overcoming one or more of the problems set forth above.